1. Field of the Invention
The present invention relates to an improved apparatus and method for making electric light sources, particularly tubular fluorescent lamps. Although the invention is of general applicability, it may be usefully combined with the invention described and claimed in U.S. Ser. No. 865,576 filed on Dec. 29, 1977 by J. P. Crenfell and S. W. Stephens.
The structure of conventional fluorescent lamps is well-known. They are generally made on high speed automatic machine groups which inter alia include stem making machines, mount mills for making mount assemblies from the stems and cathodes with their lead-in wires sealed in place, conveyors for passing the assembled mounts to a sealing machine which also receives hollow lamp tube envelopes via a further conveyor from an oven known as a "lehr" where the phosphor is baked on the inner wall of the tubes at an elevated temperature.
2. Description of the Prior Art
Known lamp sealing machines can be classified into two broad groups, namely the so-called vertical machines and horizontal machines. In a vertical machine sealing of the mounts to the ends of the lamp tube is effected sequentially: first, with the tube held vertically, a mount is sealed to the lower end of the lamp tube, the lamp tube is then removed from the sealing machine, inverted through 180.degree., reinserted in the machine and finally the second lamp mount is sealed to the other end thereof. In horizontal machines the lamp tube is held substantially horizontally and the two mounts are sealed to the ends of the lamp tube substantially simultaneously.
In addition to the broad classification into vertical and horizontal machines, the machines can also be distinguished as to their mode of operation, namely indexing or intermittent, and continuously operated machines. A further distinction arises with regard to the means employed to advance the heads in which the lamp tube and sealing burners are supported. Thus, the heads may be supported by a pair of spaced endless chain conveyors or by a pair of spaced apart rotary turrets rotating about a horizontal axis.
The present invention is applicable to all types of horizontal sealing machines with mount assemblies, "mount loading" but is most useful for high-speed, continuous, rotary turret sealing machines.
It will be obvious that the overall rate of output of an automatic fluorescent tube making machine group is closely bound up with the rate and efficiency of mount loading. While it is theoretically possible to increase the rate of delivery of mount assemblies from the mount mills to the sealing machine and to increase the number of heads and/or the rate of rotation of the sealing machine turrets, the chief problem arises at the stage of transferring the mount assembly from the conveyor and loading it into the sealing head. Essentially in all known commercially operating high speed machines the mounts must be introduced into a head of the sealing machine from the interior of the machine, i.e. from within the cylindrical space defined by the two turrets as end faces and the mantle surface which is covered by the tubular lamp envelopes that extend between the heads disposed around the turrets. Bearing in mind that the gap between circumferentially adjacent tube envelopes is desirably small in order to maximise the number of heads of the sealing machine, and bearing also in mind that the turrets rotate at a relatively high speed, the transfer of mounts from the mount conveyor heads can only be effected by introducing the mounts into the interior of the sealing machine from the conveyor heads to the sealing heads in a synchronized manner by "wasting" heads, that is to say, by leaving some heads not loaded with tubes until the turrets have rotated clear of the mount loading mechanism. Known constructions with this purpose are extremely intricate, see for example U.S. Pat. Nos. 2,721,422 Baker et al; 3,113,011--Gilbert et al, and 3,399,044--Kolkman et al. These known mechanisms all involve a plurality of mount conveyors, transfer mechanisms, associated cams and other controls.